Diesel exhaust fluid deposit mitigation

ABSTRACT

One form of the present application is an apparatus including an internal combustion engine structured to produce an exhaust flow, an exhaust system structured to receive the exhaust flow, and a reductant injector structured to inject reductant into a primary passage of the exhaust system upstream of a catalyst. The apparatus further includes an injector passage structured to receive a portion of exhaust upstream of the injector and further structured to flow the exhaust into the primary passage around the injector in a manner such that deposit formation is reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent application Ser. No. 14/512,097, filed Oct. 10, 2014, which claims priority to U.S. Provisional Patent Application No. 61/890,764, filed Oct. 14, 2013, and entitled “DIESEL EXHAUST FLUID DEPOSIT MITIGATION,” the contents of which are incorporated herein by reference in their entirety.

BACKGROUND

Selective catalytic reduction (“SCR”) exhaust aftertreatment systems are an important technology for reducing NOx, emissions from internal combustion engines. SCR systems generally include a source of storage for the diesel exhaust fluid (DEF), a doser that includes at least one of a pump unit for pressurizing the DEF and a metering unit for providing a controlled amount or rate of DEF, and an injector which provides a DEF solution to a decomposition region of an exhaust flow path located upstream from an SCR catalyst. Many SCR systems also utilize pressurized gas to assist the flow of DEF to the injector. While providing reductions in NO, emissions, SCR systems suffer from a number of shortcomings and problems.

The DEF injected into the exhaust flow may not properly mix with the exhaust flow. In some instances, the DEF can puddle along an inner wall of the exhaust system, forming a deposit over time. Thus, there is a need for advancements mitigating these and other shortcomings associated with injection systems for delivery of DEF through a nozzle connected to an exhaust system.

SUMMARY

One embodiment of the present application is a unique flow arrangement for a DEF injector. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for altering an exhaust flow to increase mixing of DEF with an exhaust flow and/or to prevent DEF deposits.

Various embodiments provide for a system including an internal combustion engine operable to produce an exhaust gas flow; a reductant injector structured to release a reductant into the exhaust gas flow; a catalyst located downstream of the reductant injector; and a bend located in a portion of an exhaust gas passageway. The exhaust gas passageway is structured to receive at least a portion of the exhaust gas flow. The bend is structured to affect a mixing of the reductant into the exhaust gas flow and/or to reduce a formation of a reductant film on an inner wall of the exhaust gas passageway.

Additional embodiments provide for an apparatus, comprising an internal combustion engine structured to produce an exhaust flow; an exhaust system structured to receive the exhaust flow; a reductant injector structured to inject reductant into a primary passage of the exhaust system upstream of a catalyst; and an injector passage structured to receive a portion of exhaust upstream of the injector. The injector passage is further structured to flow the exhaust into the primary passage around the injector in a manner such that injector tip deposit formation is mitigated.

Further embodiments provide for a method, comprising operating an internal combustion engine including a rotating assembly, whereby an exhaust flow is produced. The method further comprises selectively injecting a reductant into a main portion of the exhaust flow, and diverting a first portion of exhaust across a tip of the injector, thereby reducing reductant deposits thereon.

Still further embodiments provide for a decomposition mitigation assembly. A decomposition tube elbow includes an inner bend wall portion and an outer bend wall portion. An injector port is formed in the outer wall portion, the injector port configured to receive a reductant injector therein. An injection exhaust flow path divider wall is positioned in the decomposition tube elbow. The injection exhaust flow path divider wall forms a first pocket extending along at least a portion of the radially outer wall portion, the injector port opening to the first pocket. A bypass exhaust flow path divider wall is positioned in the decomposition tube elbow. The bypass exhaust flow path divider wall forms a second pocket extending along at least a portion of the inner bend wall portion of the decomposition tube elbow. The bypass exhaust flow path divider wall and the injection exhaust flow path divider wall form a primary exhaust flow path positioned in the decomposition tube elbow between the injection exhaust flow path divider wall and the bypass exhaust flow path divider wall.

Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary DEF delivery system.

FIG. 2 is a cross-sectional view of a flow separator disposed in combination with a DEF injector.

FIG. 3 is a cross-sectional view of another form of a flow separation device including a bend.

FIG. 4 is a cross-sectional view of a flow separator disposed into the exhaust configuration of FIG. 1.

FIGS. 5A-5C are partial cross-sectional views along various planes of the bend and flow separating annulus of FIG. 4.

FIG. 6 is a perspective view of a decomposition tube elbow, in accordance with example embodiments.

FIG. 7 is a perspective view of a decomposition tube elbow including a half mixer, in accordance with example embodiments.

FIGS. 8A-8C are a decomposition tube elbow according to further example embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, any alterations and further modifications in the illustrated embodiments, and any further applications of the principles of the invention as illustrated therein as would normally occur to one skilled in the art to which the invention relates are contemplated herein.

With reference to FIG. 1 there is illustrated an exemplary system 100 that includes a delivery system 140 for delivery of a suitable reductant 122, such as DEF to an exhaust system 115 connected to an engine 102. The system 100 may be provided on a vehicle powered by the engine 102, or on the engine 102 may be utilized in other applications such as non-vehicular power generation systems, pumping systems, or any other application which receives a useful power 110 from the engine 102. The engine 102 can be a diesel engine or any suitable internal combustion engine for which exhaust treatment with the reductant 122 is provided. The engine 102 includes an intake system 104 through which charge air enters. An exhaust gas 112, resulting from combustion, exits the engine 102 via the exhaust system 115. It should be understood that not all details of these systems that are typically present are shown. In some forms, the intake system 104 can receive pressurized air from a pressure source such as a turbocharger 114. The engine 102 can include a number of combustion chambers into which fuel is injected to combust with the charge air that has entered through an intake port in the engine 102 (not shown). The energy released by combustion causes an expansion that provides useful power transmitted via at least one piston (not shown). When used to propel a vehicle, the engine 102 is coupled through a drivetrain (not shown) to drive wheels that propel the vehicle. Intake valves (not shown) control the admission of charge air into the cylinders, and exhaust valves (not shown) control the outflow of the exhaust gas 112 through the exhaust system 115 and ultimately to the atmosphere 108. Before entering the atmosphere 108, the exhaust gas 112 is treated by one or more aftertreatment devices in an aftertreatment system 116.

In one example, the aftertreatment system 116 having one or more selective catalytic reduction (SCR) catalysts 126 and one or more locations for receiving the reductant 122, which includes, but is not limited to, diesel exhaust fluid (DEF) from the delivery system 140. The aftertreatment system 116 may include one or more other aftertreatment components, including, but not limited to, one or more oxidation catalysts, one or more particulate filters, an ammonia oxidation catalyst, and various temperature, pressure and constituent sensor of the exhaust gas 112. The intake system 104 may also include various components not shown, such as an exhaust gas recirculation (EGR) system, various heat exchangers, and other components connecting the exhaust system 115 to the intake system 104. A DEF injector 118 is mounted on a portion of the exhaust system 115 upstream of the SCR catalyst 126 having an outlet, or nozzle, arranged to spray aqueous DEF droplets 124 into the exhaust system 115 where it mixes with the exhaust gas 112 produced by the engine 102. The SCR catalyst 126 promotes a chemical reaction between the reductant 122 and NOx, in the exhaust gas 112 that converts substantial amounts of NOx to reduce NOx emissions before the exhaust gas 112 passes into the atmosphere 108.

The delivery system 140 further includes a doser 142 that receives the reductant 122 from a storage tank 120 and provides the reductant 122 to the injector 118 for injection or delivery to a decomposition chamber 134 positioned in the exhaust system 115 or directly into the exhaust system 115. As used herein, injector includes any nozzle, static device, electronically controllable device, and/or mechanical actuator that provide an outlet for DEF delivery. One example of a suitable diesel exhaust fluid comprises a solution of 32.5% high purity urea and 67.5% deionized water. It shall be appreciated, however, that other DEF solutions and reductants may also be utilized.

The doser 142 may include various structures to facilitate receipt of the reductant 122 from the storage tank 120 and the delivery of the reductant 122 to the exhaust system 115. For example, the doser 142 can include a pump and a filter screen and a check valve upstream of the pump to receive the reductant 122 from the storage tank 120. In one form, the pump is a diaphragm pump, though it shall be appreciated that any other type of pump may be utilized. The pump can output pressurized reductant 122 at a predetermined pressure which can flow through a second check valve, a pulsation dampener, and a second filter to provide pressurized reductant to a metering valve. The doser 142 can further include a bypass line around the pump having a bypass valve which is operable to open and close to permit or prevent the flow of the reductant 122 through the bypass line to a location upstream of the first filter screen where it may be returned to the storage tank 120, for example, during a purging operation.

The doser 142 can be of an airless configuration, in that the injector 118 can discharge the reductant 122 without a combined flow of pressurized air. Storage tank 120 holds a supply of the reductant 122 and can be vented to allow the reductant to be withdrawn at a port. A conduit extends from the port to the doser 142. The doser 142 is in fluid communication with the injector 118. When the doser 142 operates, it can draw the reductant 122 from the storage tank 120 through the conduit, and can pump the reductant to the injector 118. A backflow conduit (not shown) may be provided to return excess amounts of the reductant 122 to the storage tank 120. The doser 142 can be controlled through a controller 121.

FIG. 2 illustrates one form of a deposit mitigation system 202. A reduction orifice 204 is disposed within a portion of an exhaust passageway 228. The reduction orifice 204 can be structured to reduce deposits of the reductant 122 and/or to increase the reductant 122 and the exhaust gas 112 mixing. The reduction orifice 204 can be structured to increase heat transfer to an inner surface 220, to reduce an impingement of the reductant 122 upon the inner surface 220, and to reduce stagnation of droplets of the reductant 122 near the nozzle of the injector 118. When the reductant 122 is injected, some of the reductant 122 can impact the inner surface 220 of the exhaust passageway 228. If a temperature of the inner surface 220 is greater than a reductant film evaporative temperature, the reductant 122 is evaporated into the exhaust gas 112 and leaves the inner surface 220. When the reductant 122 evaporates, heat is transferred from the inner surface 220 and the surface temperature can be reduced. If the surface temperature of the inner surface 220 is less than the reductant 122 film evaporative temperature, the reductant 122 can remain on the surface and a deposit can form.

The reduction orifice 204 begins upstream of the injector 118. The reduction orifice 204 defines an injector flow path 224, a primary flow path 230, and a bypass flow path 222. The reduction orifice 204 divides the flow of the exhaust gas 112 from the engine 102 into an injector flow 208, a primary flow 206 and a bypass flow 210. In one form, the reduction orifice 204 can be of an annular configuration disposed radially outward from a centerline 236.

The reduction orifice 204 can be of any size and configuration such that, an injector flow 208 aids in mixing and discharge of a spray plume of the aqueous DEF droplets 124 into the primary flow 206 and/or a heat transfer from the exhaust gas 112 to the inner surface 220 is increased. The reduction orifice 204 can be structured to alter a velocity of the injector flow 208 and the bypass flow 210, relative to the primary flow 230, such that a reductant deposit near the injector 118 and/or on the inner surface 1220 can be mitigated or prevented. The reduction orifice 204 can include an extension 232 which is provided to divert a desired flow into the bypass flow path 222 and the injector flowpath 224. As the flow of the exhaust gas 112 approaches the reduction orifice 204, the flow of the exhaust gas 112 is divided into the bypass flow 210, the primary flow 206, and the injector flow 208. A blockage 214 located in the injector flow path 224 downstream of the injector 118 forces the injector flow 208 radially inward into the primary flow path 230. The blockage 214 can include various tapers or angles to reduce DEF drift buildup thereon. The reduction orifice 204 can further include an extension, such as lip 216 to protect the reduction orifice 204 from the spray plume of the aqueous DEF droplets 124. In operation, the injector 118 injects the reductant 122 radially inward, the spray plume of the aqueous DEF droplets 124 being carried toward the centerline 236 by the injector flow 208 and in response to the injector pressure and the primary flow 206. The injector flow 208 can provide a heated steady flow of the exhaust gas 112 across the injector 118 such that injector deposits can be reduced or prevented. The DEF spray plume of the aqueous DEF droplets 124, combined with the injector flow 208, is illustrated as a mixed flow 234.

The bypass flow 210 increases a surface temperature of the inner surface 220 of the bypass passage 222. Unlike a typical exhaust outer wall in which one surface is subject to ambient temperatures of the 108, heated exhaust can be passed over both the interior and exterior surfaces of the inner surface 220 via the bypass flow path 222 and the primary flow path 230. This increase in surface temperature can readily evaporate DEF surface puddling, and therefore can mitigate deposits along the inner surface 220.

A plurality of mixing devices 212 can be disposed downstream of the bypass flow path 222. As was previously discussed, the bypass flow path 222 can extend circumferentially about a portion of the centerline 236. The mixing devices 212 can be slits, perforations, or other features which allow the amount of bypass flow 210 to be adjusted or modeled in response to a desired mixing or wall film thickness. In some forms, the mixing devices 212 can be utilized to control the injector flow 208. Additionally, the length and circumferential extension of the bypass flow path 222 can be application specific and may be determined based upon a desired DEF film thickness and/or heat transfer from bypass flow path 222 to the inner surface 220. In some forms, the mixed flow 234, the primary flow 206, and the bypass flow 210 are combined upon exit of the decomposition chamber 134 into flow 218 to be received by the SCR catalyst 126. The mixing devices 212 in addition to a bend, to be discussed in FIG. 3, can reduce the need for additional mixing devices.

Referring now to FIG. 3, a bend 304 is illustrated in the exhaust system 115. The bend 304 is structured to impart turbulence to the flow of the exhaust gas 112 which can aid with mixing of the DEF spray of the aqueous DEF droplets 124 and/or can increase heat transfer to desired locations within the exhaust system 115. In one form, the injector 118 is located upstream of the bend. However, it is contemplated that the injector 118 be located on the bend 304 or near the bend 304 in any manner such that the bend 304 has an effect upon the DEF spray of the aqueous DEF droplets 124, missing of the DEF and/or upon the downstream DEF film. The bend 304 is illustrated as a 90 degree elbow; however, any type of bend 304 may be utilized depending upon the specific application and desired flow affect.

Illustrated at 302 is an area of the inner surface 220 where the reductant 122 may puddle. In order to prevent the aforementioned deposits at 302, bypass flow 210 can flow through passage 306 thereby increasing heat transfer from the exhaust gas 112 to the inner surface 220.

Additionally, the injector flow 208 can assist in directing the mixed flow 234 toward a centerline of the primary flow 230 away from the inner surface 220. The mixing devices 212 can further release clean (non DEF) exhaust downstream of the decomposition tube to further aid in the prevention of impingement of the reductant 122 upon the inner surface 220. The bend 304 itself, can provide a reduction in deposits through an increase in mixing the reductant 122 into the exhaust gas 112.

FIG. 4 illustrates one form of the injector 118 and the reduction orifice 204. The bend 304 approximates a 90 degree bend across an axis 402. The injector 118 can be configured to spray directly toward the inner radius 412 along the axis 402. However, it is contemplated that the injector 118 can spray+45 degrees with respect to axis 402. As was previously discussed, the primary flow 206 flows through a primary flow path 230 of the decomposition chamber 134. A portion of the exhaust gas 112 is separated into a bypass passage 222. An injector flow 208 flows through the injector flow path 224 toward the injector tip 414. The injector 118 is structured to inject DEF through an aperture 404 in the inner surface 220. The aperture 404 can be of a size sufficient to prevent any of the aqueous DEF droplets 124 from entering the injector flow path 224. A blockage 410 is structured to provide an exhaust pocket 408 within the injector flow path 224. The exhaust pocket 408 is maintained at a sufficient pressure from the injector flow 208 to prevent of the aqueous DEF droplets 124 drift into the injector flow path 224. As the injector flow 208 exits through the aperture 404, of the aqueous DEF droplets 124 drift flows with the injector flow 208; thereby, aiding in the reduction of deposit formation at the injector 118. Additionally, as the injector flow 208 and the primary flow 206 impinge on both sides of the inner surface 220, heat transfer from the flow of the exhaust gas 112 is substantially increased over a conventional exhaust system. Convection from the primary flow 206 of exhaust and bypass flow 210 also increases the heat transfer to the inner radius 412 such that any DEF which may be sprayed thereon can evaporate and reduce the likelihood of deposit formation.

Referring now to FIGS. 5A-5C, the decomposition chamber 134 of FIG. 4 is depicted. FIG. 5A illustrates a side cutaway as was shown in FIG. 4. Axis 502 and 504 are provided solely for reference purposes. Located at 506 is an injector aperture where the tip 414 of the injector 118 abuts against the exhaust passageway 228. An opening 508 of the injector flow path 208, an opening of the primary flow path 512, and an opening 510 and exit 514 of the bypass flow path are also illustrated. Referring now to FIG. 5B, the decomposition tube of FIG. 5A has been rotated 90 degrees with respect to axis 502. FIG. 5C illustrates the decomposition tube of FIG. 5A rotated 90 degrees relative to axis 504. As was aforementioned, the sizes and shapes of the openings 508, 512, 510 and of the exit 514 are application specific.

FIG. 6 is a perspective view of a decomposition tube elbow, in accordance with example embodiments. A deposit mitigation system includes a decomposition tube elbow 604. The decomposition tube elbow 604 includes an injector port 606 for receiving an injector (such as the injector 118) coupled to a doser for spraying DEF into the decomposition tube elbow 604. Specifically, an injector positioned in the injector port 606 sprays DEF into the decomposition tube elbow 604 and the DEF is transmitted through an injection inlet 607 into a primary exhaust stream flowing through a primary exhaust flow path 630. The decomposition tube elbow 604 includes an injector exhaust flow path 608, including an exhaust inlet 609 and an exhaust outlet 610. The exhaust inlet 609 receives exhaust separated from the primary exhaust stream flowing through primary exhaust flow path 630. The exhaust received via the exhaust inlet 609 and flowing through the injector exhaust flow path 608 is transmitted by the injector port 606 to warm the DEF fluid as it first leaves the injector positioned in the injector port 606 and before it descends through the injection inlet 607 into the primary exhaust flow path 630. The decomposition tube elbow 604 also includes a bypass exhaust flow path 618 positioned in an interior bend of the decomposition tube elbow 604. The bypass exhaust flow path 618 includes a bypass inlet 619 and a bypass outlet 620. The bypass exhaust flow path 618 receives exhaust separated from the primary exhaust stream flowing through primary exhaust flow path 630 to warm an interior wall surface 622 to increase heat transfer to the interior wall surface 622 and help prevent deposits from forming thereon. The decomposition tube elbow 604 also includes a full mixer 612 in the illustrated embodiments shown in FIG. 6. The full mixer 612 is configured to facilitate mixing of injected reductant and exhaust gas flowing through the decomposition tube elbow 604.

FIG. 7 is a perspective view of a decomposition tube elbow including a half mixer, in accordance with additional embodiments. In contrast to the configuration shown in FIG. 6, the decomposition tube elbow 604 includes a partial mixer including, but not limited to, a half mixer 712 positioned within the decomposition tube elbow 604.

FIGS. 8A-8C are a decomposition tube elbow according to further example embodiments. Specifically, FIG. 8A is an exterior view a decomposition tube elbow, FIG. 8B is a cross-sectional view of the decomposition tube elbow 804, and FIG. 8C is an end view of the decomposition tube elbow 804. The decomposition tube elbow includes an injector dock 811 configured to receive an injector, such as injector 118, mounted thereon. The decomposition tube elbow 804 is shown including an injector exhaust flow path 808 formed by an injection exhaust flow path divider wall 801. The injector exhaust flow path 808 includes an exhaust inlet 809 and an exhaust barrier 810. The exhaust received via the exhaust inlet 809 and flowing through the injector exhaust flow path 808 is transmitted pass the injector port 806 to warm the DEF fluid as it first leaves a injector positioned in the injector port 806 before it descends through the injection inlet 807 into a primary exhaust flow path 830. The decomposition tube elbow 804 also includes a bypass exhaust flow path 818 positioned in an interior bend of the decomposition tube elbow 804. The bypass exhaust flow path 818 is formed by a bypass exhaust flow path divider wall 802. The bypass exhaust flow path 818 includes a bypass inlet 819 and a bypass outlet 820. The bypass exhaust flow path 818 receives exhaust separated from the primary exhaust stream flowing through primary exhaust flow path 830 to warm interior wall surface 822 to increase heat transfer to the interior wall surface 822 and help prevent deposits from forming thereon.

In distinction to the decomposition tube elbow 604, the decomposition tube elbow 804 includes the primary exhaust flow path 830 where the side walls (i.e. the primary exhaust flow path walls extending between the bypass exhaust flow path 818 and the injector exhaust flow path 808) expand further radially outward between the bypass exhaust flow path 818 and the injector exhaust flow path 808 than the inner wall surfaces 822 and 823. Accordingly, the primary exhaust flow path 830 has a cross section having a variable radius and an increased cross sectional area that reduces the pressure drop for the same exhaust flow conditions. In example embodiments, the decomposition tube elbow 804 includes a mixer, including, but not limited to a full mixer extending across the entire cross section of the decomposition tube elbow 804 or a partial mixer extending across a part of the cross section of the decomposition tube elbow, such as halfway across.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain exemplary embodiments have been shown and described and that all changes and modifications that come within the spirit of the inventions are desired to be protected. It should be understood that while the use of words such as preferable, preferably, preferred or more preferred utilized in the description above indicate that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, the scope being defined by the claims that follow. In reading the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary. 

What is claimed is:
 1. A system for use with an internal combustion engine that is operable to produce an exhaust gas flow, the system comprising: a reductant injector configured to release a reductant into the exhaust gas flow; a catalyst located downstream of the reductant injector; and an exhaust gas passageway configured to receive the exhaust gas flow and having a bend, wherein the reductant injector is disposed at the bend, and wherein at least a portion of the bend is downstream from the reductant injector; wherein the exhaust gas passageway includes a primary flow path, an injector flow path separated from the primary flow path by a first wall, and a bypass flow path separated from the primary flow path by a second wall, at least a portion of each of which is located at the bend, wherein the injector flow path is located on a first side of the primary flow path, which is a side on which the reductant injector is located, and wherein the bypass flow path is located on a second side of the primary flow path, opposite the first side.
 2. The system of claim 1, further comprising an orifice disposed within the bend, wherein the orifice comprises a first flow diverter located in an interior of the exhaust gas passageway and upstream of the reductant injector, wherein the first flow diverter, in use, routes a first portion of the exhaust gas flow across a tip of the reductant injector.
 3. The system of claim 2, wherein the orifice further comprises a second flow defining the bypass flow path, the second flow diverter including an opening located upstream of the reductant injector, the opening in fluid receiving communication with a second portion of the exhaust gas flow and in fluid providing communication with the bypass pass flow path.
 4. The system of claim 3, further comprising at least one mixing device, each of the at least one mixing device disposed downstream of the reductant injector, wherein each of the at least one mixing device comprises at least one aperture in fluid receiving communication with the bypass flow path and in fluid providing communication with the exhaust gas passageway.
 5. The system of claim 1, wherein the reductant injector is disposed perpendicularly relative to the exhaust gas flow and, in use, releases the reductant towards a centerline of the exhaust gas flow.
 6. The system of claim 1, wherein the internal combustion engine is a diesel engine, wherein at least a portion of the reductant is urea, and wherein the catalyst comprises at least a portion of a selective catalytic reduction bed.
 7. The system of claim 1, wherein the reductant injector is an airless injector.
 8. The system of claim 1, further comprising a mixer disposed along a cross-sectional area of the exhaust gas passageway.
 9. The system of claim 8, wherein the mixer occupies less than a full cross-sectional area of the exhaust gas passageway.
 10. The system of claim 8, wherein the mixer occupies a full cross-sectional area of the exhaust gas passageway.
 11. The system of claim 4, wherein the bypass flow path extends annularly around at least a portion of a circumference of the exhaust gas passageway.
 12. An apparatus for use with an internal combustion engine that is operable to produce an exhaust gas flow, the apparatus comprising: an exhaust system configured to receive the exhaust flow; a reductant injector configured to inject reductant at a location upstream of a catalyst; a primary flow path; an injector flow path separated from the primary flow path by a first wall, the injector flow path being in fluid receiving communication with a first upstream location of the primary flow path relative to the reductant injector and in fluid providing communication with a portion of the primary flow path that comprises the reductant injector, in use, the injector flow path receiving a first portion of the exhaust flow upstream of the reductant injector and routing the first portion of the exhaust flow across a reductant injector tip, wherein the first portion of the exhaust flow passes through the injector flow path in parallel with the exhaust flow in the primary flow path; and a bypass flow path separated from the primary flow path by a second wall, the bypass flow path being in fluid receiving communication with a second upstream location of the primary flow path relative to the reductant injector and in fluid providing communication with a downstream location of the primary flow path relative to the reductant injector, wherein, in use, a second portion of the exhaust flow passes through the bypass flow path in parallel with the exhaust flow in the primary flow path, wherein the injector flow path is located on a first side of the primary flow path, which is a side on which the reductant injector is located, and wherein the bypass flow path is located on a second side of the primary flow path, opposite the first side.
 13. The apparatus of claim 12, wherein the reductant injector is located near a bend in the exhaust system; wherein optionally the bend is a 90 degree bend and wherein the reductant injector is located on an outer radius of the bend.
 14. The apparatus of claim 12, wherein the bypass flow path further comprises a mixer located near a bypass flow path exit. 